Built in gutters

Vaa: It is loose laid and the one picture where it overlaps the steel, it's overlapped the wrong way! Also, shingled roofs around here are getting 20 years or better. Thanks for your input on the internal corner, I hadn't thought about it giving that issue.

Tinner: Why such a short life on EPDM? I'd love to do it in copper, but I currently don't know how to make a radial bend, among other things.

I'd expect 8-10 years with EPDm. 60-100 with sweated copper seams. Leaded copper would outlast many re-roofs for 100-200 years. 20oz. copper or LLC is the only way to go. All other methods will be temporary.